On specimen geometry effects in strain-controlled low-cycle fatigue

Abstract

Strain-controlled low-cycle fatigue tests have been conducted in air at room temperature on three different specimen geometries: (1) an hourglass specimen with a minimum diameter of 10 mm; (2) a cylindrical specimen with a gauge length of 50 mm and a gauge diameter of 10 mm; and (3) a cylindrical specimen with a gauge length of 25 mm and a gauge diameter of 10 mm. The effect of specimen geometry on the cyclic stress response and fatigue life is discussed. At all the strain ranges tested the hourglass specimens showed the highest life. The 50 mm gauge-length specimen showed the least life, while the 25 mm gauge-length specimens exhibited an intermediate life. The constants and coefficients in the Coffin-Manson, Basquin and cyclic stress-strain relationships are evaluated for the three geometries. The existing models for the prediction of the fatigue ductility exponent are also applied.